// Copyright 2023 The Matrix.org Foundation C.I.C.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use std::{ops::Deref, sync::Arc};

use chrono::{Datelike, Local, TimeZone};
use imbl::Vector;
use ruma::{EventId, MilliSecondsSinceUnixEpoch};

#[cfg(doc)]
use super::controller::TimelineMetadata;
use super::{
    event_item::EventTimelineItemKind, item::TimelineUniqueId, EventTimelineItem,
    ReactionsByKeyBySender, TimelineEventItemId, TimelineItem,
};

pub(super) struct EventTimelineItemWithId<'a> {
    pub inner: &'a EventTimelineItem,
    /// Internal identifier generated by [`TimelineMetadata`].
    pub internal_id: &'a TimelineUniqueId,
}

impl EventTimelineItemWithId<'_> {
    /// Create a clone of the underlying [`TimelineItem`] with the given kind.
    pub fn with_inner_kind(&self, kind: impl Into<EventTimelineItemKind>) -> Arc<TimelineItem> {
        TimelineItem::new(self.inner.with_kind(kind), self.internal_id.clone())
    }

    /// Create a clone of the underlying [`TimelineItem`] with the given
    /// reactions.
    pub fn with_reactions(&self, reactions: ReactionsByKeyBySender) -> Arc<TimelineItem> {
        let event_item = self.inner.with_reactions(reactions);
        TimelineItem::new(event_item, self.internal_id.clone())
    }
}

impl Deref for EventTimelineItemWithId<'_> {
    type Target = EventTimelineItem;

    fn deref(&self) -> &Self::Target {
        self.inner
    }
}

#[inline(always)]
fn rfind_event_item_internal(
    items: &Vector<Arc<TimelineItem>>,
    mut f: impl FnMut(&EventTimelineItemWithId<'_>) -> bool,
) -> Option<(usize, EventTimelineItemWithId<'_>)> {
    items
        .iter()
        .enumerate()
        .filter_map(|(idx, item)| {
            Some((
                idx,
                EventTimelineItemWithId { inner: item.as_event()?, internal_id: &item.internal_id },
            ))
        })
        .rfind(|(_, it)| f(it))
}

/// Finds an item in the vector of `items` given a predicate `f`.
///
/// WARNING/FIXME: this does a linear scan of the items, so this can be slow if
/// there are many items in the timeline.
pub(super) fn rfind_event_item(
    items: &Vector<Arc<TimelineItem>>,
    mut f: impl FnMut(&EventTimelineItem) -> bool,
) -> Option<(usize, EventTimelineItemWithId<'_>)> {
    rfind_event_item_internal(items, |item_with_id| f(item_with_id.inner))
}

/// Find the timeline item that matches the given event id, if any.
///
/// WARNING: Linear scan of the items, see documentation of
/// [`rfind_event_item`].
pub(super) fn rfind_event_by_id<'a>(
    items: &'a Vector<Arc<TimelineItem>>,
    event_id: &EventId,
) -> Option<(usize, EventTimelineItemWithId<'a>)> {
    rfind_event_item(items, |it| it.event_id() == Some(event_id))
}

/// Find the timeline item that matches the given item (event or transaction)
/// id, if any.
///
/// WARNING: Linear scan of the items, see documentation of
/// [`rfind_event_item`].
pub(super) fn rfind_event_by_item_id<'a>(
    items: &'a Vector<Arc<TimelineItem>>,
    item_id: &TimelineEventItemId,
) -> Option<(usize, EventTimelineItemWithId<'a>)> {
    match item_id {
        TimelineEventItemId::TransactionId(txn_id) => {
            rfind_event_item(items, |item| match &item.kind {
                EventTimelineItemKind::Local(local) => local.transaction_id == *txn_id,
                EventTimelineItemKind::Remote(remote) => {
                    remote.transaction_id.as_deref() == Some(txn_id)
                }
            })
        }
        TimelineEventItemId::EventId(event_id) => rfind_event_by_id(items, event_id),
    }
}

/// Result of comparing events position in the timeline.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(super) enum RelativePosition {
    /// Event B is after (more recent than) event A.
    After,
    /// They are the same event.
    Same,
    /// Event B is before (older than) event A.
    Before,
}

#[derive(Debug, PartialEq)]
pub(super) struct Date {
    year: i32,
    month: u32,
    day: u32,
}

impl Date {
    pub fn is_same_month_as(&self, date: Date) -> bool {
        self.year == date.year && self.month == date.month
    }
}

/// Converts a timestamp since Unix Epoch to a year, month and day.
pub(super) fn timestamp_to_date(ts: MilliSecondsSinceUnixEpoch) -> Date {
    let datetime = Local
        .timestamp_millis_opt(ts.0.into())
        // Only returns `None` if date is after Dec 31, 262143 BCE.
        .single()
        // Fallback to the current date to avoid issues with malicious
        // homeservers.
        .unwrap_or_else(Local::now);

    Date { year: datetime.year(), month: datetime.month(), day: datetime.day() }
}
